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Publication numberUS6027452 A
Publication typeGrant
Application numberUS 08/672,218
Publication dateFeb 22, 2000
Filing dateJun 26, 1996
Priority dateJun 26, 1996
Fee statusPaid
Also published asCA2258263A1, DE69736527D1, EP0955868A1, EP0955868A4, EP0955868B1, EP1743572A1, US6632181, US6939305, US7041060, US7618375, US7951086, US20020099296, US20040077956, US20060004293, US20060206030, US20100056930, US20110263990, WO1997049328A1
Publication number08672218, 672218, US 6027452 A, US 6027452A, US-A-6027452, US6027452 A, US6027452A
InventorsBryan Patrick Flaherty, Mark Henry Sher, Richard G. Caro
Original AssigneeVital Insite, Inc.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Rapid non-invasive blood pressure measuring device
US 6027452 A
Abstract
A blood pressure can be obtained by supplying an external pressure to a portion of an artery. The external pressure is preferably between the systolic and diastolic pressure. An event which occurs at least once a cycle can then be identified. This event can be, for example, a peak in the arterial compliance that occurs at a transmural pressure approximately equal to zero. A pair of signals, one that is an arterial volume-indicating signal, and one that is an arterial pressure-indicating signal can be used to identify this event. Alternately, a small signal high-frequency exciter component can be placed upon the pressure or volume of the artery and detected to determine the time that the transmural pressure is equal to zero.
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Claims(89)
What is claimed is:
1. An apparatus comprising:
a device for applying external pressure to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle; and
a processor adapted to identify an event occurring at a transmural pressure in said range of transmural pressures, the event being associated with a first time, the arterial pressure at said first time not being a systolic or diastolic arterial pressure, the processor further adapted to determine the arterial pressure at a specific time.
2. The apparatus of claim 1, wherein the device varies the external pressure during the cardiac cycle less than the average difference between systolic and diastolic pressure.
3. The apparatus of claim 1, wherein the range in the transmural pressure is primarily due to arterial pressure variation.
4. The apparatus of claim 1, wherein the device applies the external pressure to an artery over a measurement period.
5. The apparatus of claim 4, wherein the device applies a substantially constant external pressure to the artery over the measurement period.
6. The apparatus of claim 5, wherein the substantially constant pressure-applying device comprises a cuff that contains a constant volume of a fluid during the measurement period.
7. The apparatus of claim 5, wherein the processor is adapted to determine said first time that the event occurs without requiring data from outside the measurement period.
8. The apparatus of claim 4, wherein the processor is adapted to determine said first time that the event occurs without requiring data from outside the measurement period.
9. The apparatus of claim 1, wherein the device applies an external pressure not equaling a systolic or diastolic arterial pressure over the cardiac cycle.
10. The apparatus of claim 1, wherein the processor is adapted to determine the arterial pressure at the first time.
11. The apparatus of claim 1, wherein specific time is not the first time.
12. The apparatus of claim 1, further comprising a detector to produce a pressure-indicative signal, wherein the processor is further adapted to calibrate the pressure-indicative signal using the arterial pressure at the specific time.
13. The apparatus of claim 12, wherein the detector is an arterial tonometer.
14. The apparatus of claim 12, wherein the detector is a pressure sensor of a vascular unloading system.
15. The apparatus of claim 1, wherein the processor is adapted to calibrate a pressure-indicative signal using the arterial pressure at the specific time.
16. The apparatus of claim 15, further comprising a pressure wave velocity measurement system to produce the pressure indicative signal.
17. The apparatus of claim 1, wherein the processor is adapted to identify a peak in arterial compliance.
18. The apparatus of claim 1, wherein the processor is adapted to identify the opening or closing of the artery.
19. The apparatus of claim 1, wherein the processor is adapted to identify a change in the viscoelastic properties of a portion of the body.
20. The apparatus of claim 1, wherein the processor is adapted to identify a change in the flow of blood through the artery.
21. The apparatus of claim 1, wherein the processor is adapted to identify an event occurring at a transmural pressure of about zero.
22. The apparatus of claim 1, further comprising a first detector electrically connected to the processor to produce a signal indicative of arterial pressure and a second detector electrically connected to the processor to produce a signal indicative of an arterial volume.
23. The apparatus of claim 22, wherein the processor is adapted to determine the first time of the event from the pressure-indicative signal and the volume-indicative signal.
24. The apparatus of claim 22, wherein the processor is adapted to evaluate volume-indicative values versus pressure-indicative values to help determine a time when the transmural pressure is equal to about zero.
25. The apparatus of claim 22, wherein the first detector comprises a tonometer.
26. The apparatus of claim 22, wherein the first detector comprises an apparatus to measure the velocity of a pressure wave in the artery.
27. The apparatus of claim 22, wherein the second detector comprises a plethysmograph.
28. The apparatus of claim 22, wherein the second detector comprises a pressure transducer on a cuff used to supply the external pressure.
29. The apparatus of claim 1, wherein the processor is adapted to sample signals of external physiological indications.
30. The apparatus of claim 1, further comprising a detector to produce a volume-indicative signal, wherein the processor is further adapted to compare the volume-indicative signal measured with two different external pressures to determine a blood pressure at a time.
31. The apparatus of claim 30, wherein the processor is further adapted to compare the volume-indicative signals at two different time periods, the one of the time periods being such that an external pressure between the systolic and diastolic is applied to sections of the artery.
32. The apparatus of claim 1, further comprising a detector used to detect a signal indicative of the arterial closing or opening.
33. An apparatus comprising:
a device for applying external pressure to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle;
a processor adapted to identify an event occurring at a transmural pressure in said range of transmural pressures, the event being associated with a first time, the processor further adapted to determine the arterial pressure at a specific time; and
an exciter to induce an oscillating component having a frequency greater than the pulsatile frequencies.
34. The apparatus of claim 33, wherein the exciter induces an oscillating component onto the arterial pressure.
35. The apparatus of claim 33, further comprising a detector to produce a signal indicative of arterial volume.
36. The apparatus of claim 35, further comprising a filter to filter the signal indicative of arterial volume.
37. The apparatus of claim 33, further comprising a detector to produce a signal indicative of arterial pressure.
38. The apparatus of claim 33, further comprising means to put the oscillatory component onto the arterial volume.
39. The apparatus of claim 38, wherein the external pressure-applying means is a cuff for applying external pressure to a section of an artery, the cuff having a chamber adapted to contain a fluid, the oscillatory component means comprising means to produce an oscillation in volume of the fluid of the cuff.
40. A method of determining arterial pressure, comprising:
applying an external pressure to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle;
identifying an event occurring at a transmural pressure in said range of transmural pressures, the event being associated with a first time, the arterial pressure at said first time not being a systolic or diastolic arterial pressure; and
determining the arterial pressure at a specific time.
41. The method of claim 40, wherein the external pressure varies during the cardiac cycle less than the average difference between systolic and diastolic pressure.
42. The method of claim 40, wherein the range in the transmural pressures is primarily due to arterial pressure variation.
43. The method of claim 40, wherein the external pressure is applied to the artery over a measurement period.
44. The method of claim 43, wherein said first time that the event occurs is determined without requiring data from outside the measurement period.
45. The method of claim 43, wherein the device applies a substantially constant external pressure to the artery over the measurement period.
46. The method of claim 45, wherein the substantially constant pressure-applying device comprises a cuff that contains a constant volume of a fluid during the measurement period.
47. The method of claim 40, wherein the external pressure is not equal to a systolic or diastolic arterial pressure over the cardiac cycle.
48. The method of claim 40, wherein the arterial pressure is determined at the first time.
49. The method of claim 40, wherein specific time is not the first time.
50. The method of claim 40, further comprising producing a pressure-indicative signal, and calibrating the pressure-indicative signal using the arterial pressure.
51. The method of claim 50, wherein the pressure-indicative signal is produced with an arterial tonometer.
52. The method of claim 50, wherein the pressure-indicative signal is produced with a pressure sensor of a vascular unloading system.
53. The method of claim 40, further comprising calibrating a pressure-indicative signal using the arterial pressure.
54. The method of claim 53, wherein the pressure-indicative signal is produced by a pressure wave velocity measurement system.
55. The method of claim 40, further comprising identifying a peak in arterial compliance.
56. The method of claim 40, further comprising identifying the opening or closing of the artery.
57. The method of claim 40, further comprising identifying a change in the viscoelastic properties of a portion of the body.
58. The method of claim 40, further comprising identifying a change in the flow of blood through the artery.
59. The method of claim 40, further comprising identifying an event occurring at a transmural pressure of about zero.
60. The method of claim 40, further comprising producing a signal indicative of arterial pressure and producing a signal indicative of an arterial volume.
61. The method of claim 60, wherein the first time of the event is determined from the pressure-indicative signal and the volume-indicative signal.
62. The method of claim 61, further comprising evaluating volume-indicative values versus pressure-indicative values to help determine a time when the transmural pressure is equal to about zero.
63. The method of claim 60, wherein the pressure-indicative signal is produced by a tonometer.
64. The method of claim 60, wherein the pressure-indicative signal is produced by an apparatus to measure the velocity of a pressure wave in the artery.
65. The method of claim 60, wherein the volume-indicative signal is produced by a plethysmograph.
66. The method of claim 60, wherein the volume-indicative signal is produced by a pressure transducer on a cuff used to supply the external pressure.
67. The method of claim 40, further comprising sampling signals of external physiological indications.
68. The method of claim 40, further comprising producing a volume-indicative signal, and comparing the volume-indicative signal measured with two different external pressures to determine a blood pressure at a time.
69. The method of claim 68, further comprising comparing the volume-indicative signals at two different time periods, the one of the time periods being such that an external pressure between the systolic and diastolic is applied to a section of the artery.
70. The method of claim 40, further comprising a detecting a signal indicative of the arterial closing or opening.
71. A method of determining arterial pressure, comprising:
applying an external pressure to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle;
inducing an oscillating component having a frequency greater than the pulsatile frequencies;
identifying an event occurring at a transmural pressure in said range of transmural pressures, the event being associated with a first time; and
determining the arterial pressure at a specific time.
72. The method of claim 71, wherein the oscillating component is induced onto the arterial pressure.
73. The method of claim 72, further comprising producing a signal indicative of arterial volume.
74. The method of claim 73, further comprising filtering the signal indicative of arterial volume.
75. The method of claim 71, further comprising producing a signal indicative of arterial pressure.
76. The method of claim 71, further comprising imposing the oscillatory component onto the arterial volume.
77. The method of claim 76, wherein the external pressure-applying step is done with a cuff for applying external pressure to a section of an artery, the cuff having a chamber adapter to contain a fluid, further comprising oscillating the volume of the fluid of the cuff.
78. An apparatus comprising:
a device for applying external pressure to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle, the device applying a substantially constant external pressure to the artery over the measurement period; and
a processor adapted to identify an event occurring at a transmural pressure in said range of transmural pressures, the event being associated with a first time, the processor further adapted to determine the arterial pressure at a specific time, wherein the processor is adapted to determine said first time that the event occurs without requiring data from outside the measurement period.
79. The apparatus of claim 78, wherein the substantially constant pressure-applying device comprises a cuff that contains a constant volume of a fluid during the measurement period.
80. The apparatus of claim 78, wherein the device applies an external pressure not equaling a systolic or diastolic arterial pressure over the measurement period.
81. The apparatus of claim 78, wherein the processor is adapted to identify a peak in arterial compliance.
82. The apparatus of claim 78, wherein the processor is adapted to identify an event occurring at a transmural pressure of about zero.
83. A method of determining arterial pressure comprising:
applying an external pressure to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle, a substantially constant external pressure being applied over a measurement period;
identifying an event occurring at a transmural pressure in said range of transmural pressures, the event being associated with a first time; and
determining the arterial pressure at a specific time without requiring data from outside the measurement period.
84. The method of claim 83, wherein the substantially constant pressure-applying device comprises a cuff that contains a constant volume of a fluid during the measurement period.
85. The method of claim 83, wherein the external pressure is not equal to a systolic or diastolic arterial pressure over the measurement period.
86. The method of claim 83, further comprising identifying a peak in arterial compliance.
87. The method of claim 83, further comprising identifying an event occurring at a transmural pressure of about zero.
88. An apparatus comprising:
a device for applying external pressure to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle; and
a processor adapted to identify an event occurring at a transmural pressure in said range of transmural pressures, the event being associated with a first time, the processor further adapted to determine the arterial pressure at a specific time, the processor being adapted to determine the arterial pressure at the specific time without requiring data from outside the cardiac cycle.
89. A method of determining arterial pressure, comprising:
applying an external pressure to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle;
identifying an event occurring at a transmural pressure in said range of transmural pressures, the event being associated with a first time; and
determining the arterial pressure at a specific time without requiring data from outside the cardiac cycle.
Description
BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatus for the non-invasive determination of blood pressure.

Direct measurement of blood pressure with a pressure measuring device such as a tonometer is difficult in a clinical setting. A problem with tonometer readings is that although the times of the systolic and diastolic pressures are correct, the pressure readings may have an incorrect scaling or have an offset in the recorded pressure. Tonometer measurements can depend on the position of the tonometer, artery and bone structure behind the artery.

Another prior art system used to determine arterial pressures is an automated oscillometric device called a "Dinamap" (device for indirect non-invasive mean arterial pressure). This device is described in a paper entitled "Arterial Pressure Monitoring: Automated Oscillometric Devices"; M. Ramsey III; Journal of Clinical Monitoring; Volume 7, No. 1; January 1991; pp. 56-67. This system uses a cuff to supply an external pressure to an artery. The cuff pressure is stepped in increments from a pressure believed to be above the systolic pressure to a pressure believed to be below the diastolic pressure. An arterial volumetric indication is monitored by the system. For example, a pressure transducer attached to the cuff will give some indication of the volume of the artery, since the pressure in the cuff will be greater when the artery volume is high. When the mean value of the arterial blood pressure is about the same as the external cuff pressure, the amplitude of the variations of the volumetric indication will be the greatest. In this way, an indication of the mean arterial pressure can be obtained. A disadvantage of this prior art system is the considerable time it takes to obtain the arterial pressure information. Many cardiac cycles are needed to obtain the data required to determine a blood pressure.

An alternative system is described in "Vibration Technique for Indirect Measurement of Diastolic Arterial Pressure in Human Fingers"; Shimazu, et al.; Medical and Biological Engineering in Computing; March 1999; Volume 27; pp. 130-136. This paper describes a method for obtaining a diastolic pressure which is somewhat similar to the oscillometric technique used with the Dinamap. In the Shimazu, et al. system, a small oscillation is placed on the cuff pressure. A plethysmograph is used to get a volumetric indication of the volume of the artery. The output of the plethysmograph will show a high-frequency component imposed on a pulsatile component. The cuff pressure is ramped or stepped in a manner similar to the Dinamap system. In the cardiac cycle where the cuff pressure is roughly equal to the diastolic pressure, the amplitude of the high-frequency component of the volumetric indication will be greater in the diastolic period of that cycle than at the diastolic period of any other cycle. In this way, the diastolic pressure can be determined. Like the Dinamap system, the Shimazu, et al. system is relatively slow. Many cardiac cycles are required to determine a single blood pressure value.

Another prior art system is described in Penaz U.S. Pat. No. 4,869,261. Penaz describes a vascular unloading system. Vascular unloading systems attempt to cause the external applied pressure to be equal to the arterial blood pressure at all times. These systems use a plethysmograph and a feedback loop in order to adjust the external pressure so that it tracks the arterial pressure. A disadvantage of this system is that, when the external pressure tracks the arterial pressure, the mean applied pressure is relatively high. For this reason, the system described in Penaz may be uncomfortable or painful to use. Additionally, vascular unloading systems tend to produce a pressure signal that is off from the real arterial pressure by a DC offset.

The systems of Palti U.S. Pat. No. 4,660,544 and Sramek U.S. Pat. No. 4,343,314 use very fast ramped external pressures. A disadvantage of these systems is that the required very fast ramped pressures may be impractical to produce. In particular, it may be difficult to use a cuff to apply the external pressures because of the relatively long periods of time required to inflate or deflate a cuff. Additionally, the quick external pressure ramp could be uncomfortable.

Therefore, it is desired to have a method and apparatus for obtaining a blood pressure that can avoid long measurement times or high applied external pressures.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for quickly determining a blood pressure value at a specific time. An external pressure is supplied to the artery so that the artery experiences a range of transmural pressures. The external pressure is set so that a known event, or marker, will occur during a measurement period. The measurement period is a short period of time that typically can be a cardiac cycle or a few cardiac cycles. The value of the external pressure at the time of the event allows for the calculation of an arterial pressure associated with the time of the event or an earlier or later time in another cardiac cycle.

By allowing a range of transmural pressures within a cardiac cycle, the transmural pressure is not clamped at zero like in the apparatus of the Penaz patent. In one embodiment, the range in the transmural pressure is mainly due to arterial pressure variations.

Examples of events, or markers, that can be detected include a peak in the arterial compliance curve at the transmural pressure about equal to zero or an opening or closing of an artery. Other markers that can be used include a pressure dependant change in attenuation of a propagating pressure wave; frequency dependent effects (i.e. level of attenuation of a propagating wave versus frequency or a compliance versus frequency relationship); changes in a compliance versus attenuation relationship; a change in the viscoelastic properties of the artery or other portion of the body; or a change in the flow of blood through the artery.

Several of the preferred embodiments of the invention use, as a marker, the peak in the compliance of the artery. The peak is, by definition, the transmural pressure (or pressure across the artery wall) where the slope of the pressure-volume relationship of the artery is the steepest. The pressure-volume relationship relates the pressure across the artery wall to the volume in the lumen of the artery. The peak in the compliance indicates that, at that transmural pressure, a given change in transmural pressure will cause a larger change in the volume of the artery than at any other transmural pressure. This peak is thought to occur at a transmural pressure of zero because the artery wall is at the least amount of stress at this pressure.

It is possible that the peak in compliance does not occur at zero transmural pressure, but rather at some transmural pressure close to zero. These slight variations could be caused by a number of factors including: arterial size, presence of disease states, age, gender, etc. The system of the present invention can produce relatively accurate blood pressure values when it assumes the compliance peak occurs at the transmural pressure of zero. If significant variations in the transmural pressure of peak compliance are found to occur, this invention would still function adequately if an appropriate compensating factor were added to the measured pressure.

The time that an event (i.e. transmural pressure approximately zero) occurs is used to produce an indication of the arterial blood pressure at a specific time. For example, if the transmural pressure is equal to zero at time T1, the system knows that the arterial pressure is equal to the cuff pressure at time T1 and/or at a different time with the same position in a subsequent or prior cardiac cycle as T1.

Within as little as single cardiac cycle, all of the data required to determine a blood pressure at a certain time can be obtained. This is much quicker than the many cycles required in the Dinamap and Shimazu systems.

The information of a blood pressure at a certain time can be used to calibrate a blood pressure signal, such as a signal from an arterial tonometer, a pressure wave velocity measurement system, or a vascular unloading device. Alternatively, it may be useful just to have any blood pressure in some situations, especially since the present invention can determine a blood pressure so quickly.

In the present invention, it is not necessary for large changes to be made to the external applied pressure. For this reason, the control of the external pressure is made easier. For example, the external pressure can be applied by a cuff which is inflated with a fluid, such as air or water, to a constant volume. The external pressure would thus be substantially constant.

Some embodiments of the present invention use the fact that there is a peak to the compliance versus pressure curve at a transmural pressure approximately equal to zero. This means that at a transmural pressure approximately equal to zero, small arterial pressure changes can cause large arterial volume changes. These embodiments preferably use an external pressure between the systolic and diastolic pressure. This external pressure can be less than the peak external pressures used in the Dinamap or Penaz systems.

One set of embodiments using this relationship uses an arterial pressure dependent signal and an arterial volume dependent signal to produce a curve of a volume indication versus a pressure indication. These embodiments are called pressure/volume embodiments. The maximum rate of change of this curve will be at a transmural pressure approximately equal to zero. Alternately, the curve can be fitted to a polynomial equation. A derivative of the polynomial equation can be obtained to get an equation that is related to the compliance. A maximum of this compliance equation would be at a transmural pressure approximately equal to zero. This means that, when the arterial pressure dependent signal has a value such that the compliance related value has a maximum, the arterial pressure is approximately equal to the externally-applied pressure. The time at which the transmural pressure is approximately equal to zero is obtainable, since the system knows the value of the pressure-dependent signal at different times.

These embodiments can also work if there is a non-linear dependence of the pressure-dependent signal or volume-dependent signal to the actual arterial pressure or arterial volume. This is because, in the present embodiment, only a maxima or maximum rate of change of a curve is required to be determined.

Examples of arterial pressure-dependent signals that can be used include a tonometer or other pressure sensors, or a system which measures the velocity of wave propagation in the artery. The pressure wave velocity is monotonically-related to the arterial pressure. Alternately, a pressure signal from a vascular unloading device could be used as a pressure dependent signal.

The volume-dependent signal can be obtained from a plethysmograph. Alternatively, the volume-dependent signal can be obtained from a pressure transducer connected to the cuff used to provide the external pressure. Increases in the arterial volume will cause the pressure within the cuff to increase. Decreases in arterial volume will cause the pressure in the cuff to decrease.

Another set of embodiments of the present invention use an exciter to put a high frequency pressure signal onto the blood pressure or the external pressure. This set of systems will then look at a volume-related signal to obtain an indication of the time that the transmural pressure is equal to zero. The input signal is at a higher frequency than the pulsatile components. The pulsatile components generally have relatively low frequencies. The volume-related signal can be filtered so that the high frequency output of the volume-related signal is obtained. The greatest amplitude of this high frequency signal will be at a point of the cycle in which the transmural pressure is equal to zero. The time within a cardiac cycle that the transmural pressure is equal to zero can be obtained with a precision that depends on the frequency of the exciter signal. The volume-related signal such as a plethysmograph can be filtered with a high-pass filter to get the high frequency component.

Another set of embodiments use a system identification approach. For example, a constant amplitude volume oscillation to the volume of the external pressure cuff can cause a volume change of the artery. A pressure indicative signal can be filtered to obtain the high-frequency component. The minimum amplitude of this high frequency component of the pressure changes would occur at the time of maximum compliance. Other alternative embodiments are also possible.

Yet another set of embodiments concern the arterial closing or opening. The arterial opening and closing will usually occur at a certain transmural pressure. A high frequency pressure signal can be sent towards an artery that has an applied external pressure. When the artery closes, the signal will be blocked and/or reflected. This means that the external pressure can be set such that within a cardiac cycle, a time can be obtained that the artery opens or closes.

Another embodiment uses a critical value associated with viscosity. Pressure wave velocity measuring system can be used to produce an indication of the attenuation of the pressure signal that is related to the viscosity. A critical value in the viscosity can be used such that by looking at the attenuation of the pressure signal an arterial pressure can be obtained.

In another embodiment, it an event can be identified in a pressure wave that propagates through tissue other than the artery, such as bones, skin, muscle, tendon, etc. For this system, the transfer function is calculated for the portion of the detected pressure wave signal that travels via paths other than the artery. The marker can be obtained by the change in the relationship between phase, amplitude and frequency, of the propagated pressure. Another embodiment of the present invention uses the existence of harmonics to determine a certain specific time at which the arterial pressure has a certain value. Non-linear transfer functions, such as the arterial-volume/transmural-pressure curve, can cause harmonics to be produced. This means that a detector using a band-pass filter set at a frequency which is a multiple of an input exciter frequency will produce a signal that can give information about a critical transmural pressure, such as the transmural pressure equal to zero.

Additionally, blood flow can be manipulated to produce a marker at a particular transmural pressure. For example, the peak flow velocity in a section of artery increases if the compliance of a distal segment of the artery were decreased. The compliance of a distal section of the artery can be changed by applying an external pressure, and would have a maximum at a transmural pressure of zero. Other changes are measured if the flow meter is placed immediately distal to the segment of the artery where the transmural pressure was manipulated. The measurements of the blood flow can be done with a Doppler flow meter.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and aspects of the present invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of the apparatus of the present invention.

FIG. 2 is a flow chart illustrating the method of the present invention.

FIG. 3 is a diagram illustrating the use of the present invention in a simultaneous measurement system.

FIG. 4 is a diagram illustrating the method of the present invention used in a sequential measurement system.

FIG. 5 is a diagram illustrating an embodiment of the present invention using a tonometer to produce a pressure-indicative signal and a plethysmograph to produce a volume-indicative signal.

FIGS. 6A-D are graphs illustrating the operation of the embodiment of the present invention shown in FIG. 5.

FIG. 7 is a flow chart illustrating the operation of the processor used in the embodiment of FIG. 5.

FIG. 8 is a diagram illustrating an embodiment of the present invention using an externally-applied signal and obtaining an arterial volume-related signal with the use of a plethysmograph.

FIG. 9 is a diagram of an apparatus of the present invention using an exciter and a pressure transducer attached to a cuff to obtain an arterial volume indicative signal.

FIG. 10 is a graph illustrating the relationship between cross-sectional area or volume and the transmural pressure.

FIGS. 11A-C are graphs illustrating the operation of the embodiments of FIGS. 8 or 9.

FIG. 12 is a flow chart illustrating the operation of the processor of FIG. 8.

FIG. 13 is a diagram illustrating an embodiment of the present invention using a constant volume high-frequency input to the cuff.

FIG. 14 is a graph illustrating the dependence of cross-sectional area or volume with respect to the transmural pressure.

FIGS. 15A-D are graphs illustrating the operation of the apparatus of FIG. 13.

FIG. 16 is a flow chart illustrating the operation of a processor used in FIG. 13.

FIG. 17 is a diagram illustrating an embodiment of the present invention in which a velocity-dependent measurement is made with the exciter and detector for the velocity determining operation being placed underneath an external pressure-applying cuff.

FIG. 18 is an illustration of the velocity of propagation of a pressure wave versus the transmural pressure in the artery.

FIGS. 19A-B are graphs illustrating the embodiment of FIG. 17.

FIG. 20 is a flow chart illustrating the operation of the processor of FIG. 17.

FIG. 21 is a diagram illustrating an embodiment of the present invention in which a pressure wave velocity is determined to obtain a pressure-related signal outside of the external pressure-applying cuff and a volume-related signal is obtained by the plethysmograph inside of the external pressure-applying cuff.

FIGS. 22A-D illustrate the operation of the embodiment of FIG. 21.

FIG. 23 is a diagram illustrating an embodiment of the present invention that operates to determine the time that an artery is opened or closed.

FIGS. 24A-C are graphs illustrating the operation of the embodiment of FIG. 23.

FIG. 25 is a diagram illustrating an alternate embodiment of the present invention that operates to determine the time that an artery is opened or closed.

FIGS. 26A-B are graphs illustrating the operation of the embodiment of FIG. 25.

FIG. 27 is a diagram of an apparatus of the present invention using a plethysmograph to obtain an arterial volume-indicative signal in two different cardiac cycles with two different external pressures.

FIG. 28 is a graph illustrating the relationship between volume and the transmural pressure.

FIGS. 29A-C are graphs illustrating the operation of the embodiment of FIG. 27.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a diagram of an apparatus 30 of the present invention. This embodiment uses an external pressure-applying device 32, which applies an external pressure onto an artery 34a in a part of the body 34. Also shown is a bone 34b behind the artery 34a. The external pressure-applying device can be, for example, a cuff, such as a Duracuff available from Critikon. Any other device providing a controlled external pressure could also be used. A detector 36 can be used to detect a physiological signal. In some of the embodiments described below, detector 36 will be used to obtain an arterial pressure-indicative signal or an arterial volume-indicative signal.

Optionally, an exciter 38 can be used to produce an induced high-frequency perturbation on the artery that can be detected by the detector 36. The output of the detector 36 may be filtered. The detector 36 can be positioned at positions A, B or C shown in the figure.

A processor 40 is used to analyze the data obtained by the detector or detectors. The processor can be, for example, a computer with appropriate hardware to capture analog signals, such as an IBM PC with an analog-to-digital converter. Alternatively, a dedicated processor could be used.

FIG. 2 is a flow chart illustrating the method of the present invention. In step 42, an external pressure is applied to an artery, the external pressure being such that the artery experiences a range of transmural pressures within a cardiac cycle. Allowing a range of transmural pressures within a cardiac cycle can help avoid some of the difficulties of the system of the Penaz patent. In some embodiments, the range of transmural pressures is produced by applying a substantially constant external pressure to a section of the artery.

Steps 44-46 are preferably done by the processor 40. In step 44, an event occurring at a transmural pressure in said range of transmural pressures is identified, the event being associated with a first time. The event can be, for example, a peak in the arterial compliance curve at the transmural pressure equal to zero. The event could also the closing or opening of an artery. In some embodiments, the time is determined without requiring data from outside a measurement period.

As will be described below with respect to the specific embodiments, this step can be done in a variety of ways. For example, data from a pressure-indicative signal and a volume-indicative signal can be used to produce a curve which indicates a time at which the transmural pressure is equal to zero, or an exciter signal component can be used to indicate a time within a cardiac cycle at which the transmural pressure is zero.

In step 46, the arterial pressure is at a specific time determined. This specific time can be the time of the event identified, or it can be another time. For example, the time of the event can be measured in terms of a percentage of the cardiac cycle time from a diastolic pressure. Thus, at another time outside of the measurement period, it can be determined that at a specific time which is the same percentage of a cardiac cycle from the diastolic pressure, the arterial pressure is the determined value.

FIGS. 3 and 4 are flow charts illustrating different ways of using an arterial pressure indication produced by the present invention to calibrate a pressure-tracking signal. In the simultaneous measurement system of FIG. 3, at the same time an external pressure is applied in step 52, and the marker event measured in step 54, a pressure-tracking signal is determined in step 56. For example, the pressure-tracking signal can be a signal from a tonometer; a pressure wave velocity determination where the pressure wave velocity is linearly related to the pressure; or the signal from a vascular unloading device. In step 58, the pressure marker, that is, the indication of a blood pressure at a time, can be used to calibrate the pressure-tracking signal. In the sequential measurement system of FIG. 4, the pressure-tracking signal is recorded in step 60, an external pressure is applied in step 62, a measured event determined in step 64. Next a pressure-tracking signal is recorded again in step 66, and in step 68, the pressure marker is used to calibrate the pressure-tracking signal. Sequential measurement, as described in FIG. 4, would be advantageous for systems in which the application of the external pressure for determining the marker event would prevent an accurate pressure tracking signal.

The pressure signal to be calibrated can be from an arterial tonometer, a pressure wave velocity measurement system or a vascular unloading system.

FIG. 5 is a diagram of an apparatus 70 using a tonometer 72 to produce a pressure-indicative signal and a plethysmograph 75 to produce an arterial volume-indicative signal. Although the tonometer 72 gives an arterial pressure indication, tonometers by themselves are typically not sufficiently accurate. The tonometer readings depend upon their placement with respect to the artery and the underlying bone. For that reason, the readings of the tonometer cannot accurately be used to produce an actual arterial pressure. A cuff engine 74 can be used to inflate a cuff to a desired pressure, as indicated by the pressure transducer 76. The cuff pressure is inflated to the desired external pressure.

In a preferred embodiment, the cuff 78 is inflated to produce an external pressure such that the desired event will occur at least once during each cycle. If the desired event to be identified is the transmural pressure equal to zero, the external pressure is maintained at a value between the systolic and diastolic pressure. Such an external pressure will be relatively easy to estimate. Additionally, the externally applied pressure can be modified over different cardiac cycles to find a pressure between the diastolic and the systolic.

The plethysmograph can be a photo-plethysmograph such as a device that uses an light emitting diode (LED) or other light source to shine light through an artery to a detector. A change in the artery volume changes the transmission of the light through the artery, producing an arterial volume indicative signal. The plethysmograph could also be an impedance plethysmograph. An impedance plethysmograph sends an electrical signal through an artery so that the detected signal provides an indication of the arterial volume. Additionally, a piezoelectric plethysmograph, pressure or displacement transducers or strain gages can be used.

FIGS. 6A-D illustrate the operation of the apparatus 70 of FIG. 5. FIG. 6A is a pressure-indicative signal from a tonometer. FIG. 6B illustrates a volume-indicative signal from a plethysmograph. These signals can be used to produce a curve of volume versus pressure shown in FIG. 6C. The processor can associate a measured pressure with a measured volume occurring at the same time. For example, the measured pressure Pa occurs at the same time Ta as the measured volume Va, and the measured pressure Pb occurs at the same time Tb as the measured Vb. From such measured pressure/measured volume pairs, a graph such as the graph of FIG. 6C can be produced. In this graph, the greatest rate of change of the measured volume versus measured pressure will occur at a pressure Px which is associated with the time Tx. It is known that the greatest rate of change of an arterial volume versus arterial pressure occurs at the transmural pressure equal to zero. Thus, the transmural pressure would be equal to zero at time Tx and the arterial pressure is equal to the applied external pressure at this time.

Alternately, the graph of FIG. 6A can be fitted to a polynomial equation and a derivative equation produced. FIG. 6D is a graph of compliance versus measured pressure obtained with the derivative equation. At the maximum of the compliance equation, at a pressure Px (associated with time Tx), the transmural pressure is equal to zero.

Thus, the present invention allows for an arterial pressure indication to be produced from data obtained over as little as a single cardiac cycle. This arterial pressure indication is not necessarily the systolic and diastolic pressure. This arterial pressure indication can be used to calibrate a pressure-indicative signal.

Looking again at FIG. 6A, assuming that the tonometer is off from the real pressure value by a scale constant C1, and an offset constant C2. The equation

real arterial pressure=C1 measured pressure+C2 

will apply. The tonometer can be calibrated with two determinations of the real pressure obtained at different cuff pressures. For example, assuming at time Tx, the real pressure RPx, is equal to the cuff pressure, CPx, and the measured pressure is MPx ; and at time Ty, the real pressure RPy is equal to the cuff pressure, CPy, and the measured pressure is MPy, then ##EQU1## Alternatively, the processor could use other well-known algorithms to scale the arterial pressure indicative signal.

If the vascular unloading system is used, the method of the present invention can be used to provide the correct DC offset.

A system that operates in a similar manner to that described with respect to FIGS. 5 and 6 is described below with respect to FIGS. 21 and 22. The system of FIGS. 21 and 22 uses a pressure wave velocity signal to give an indication of the arterial pressure.

FIG. 7 is a flow chart illustrating the operation of the processor 80 of FIG. 5. In step 90, the tonometer, plethysmograph and time are sampled. The time can be a time derived from a clock signal. In step 92, ordered pairs of the sampled volume and sampled pressure can be formed into a graph of measured volume versus measured pressure as shown in FIG. 6C. In step 94, the graph is fitted with a polynomial equation that gives volume in terms of pressure. Such a polynomial fitting to a graph is a well-known data-processing technique. In step 95, a derivative of the polynomial equation can be produced. The production of a derivative equation from a polynomial equation is well known. The derivative equation will give compliance indication with respect to a measured pressure. In step 96, the maximum of the compliance is used to give the measured pressure at which the transmural pressure is zero. This means that the arterial blood pressure is equal to the external applied pressure. A time associated with the measured pressure at the maximum is attained. In the optional step 98, the time and the pressure reading is used to calibrate a tonometer output. This can be done by producing a constant by which all the tonometer readings are multiplied.

FIG. 8 illustrates an exciter system 100 using the exciter 102 to produce an induced high-frequency signal which is detected by plethysmograph 104. In one embodiment, the plethysmograph produces a volumetric indication which is filtered by the high-pass filter 106 to isolate the high-frequency component induced by the exciter 102. This high-frequency indication is sent to the processor 80. In a preferred embodiment, a 40 Hertz oscillator 108 is used to produce an electrical signal to control the exciter 102 so that a 40 Hertz pressure wave signal is imposed on the blood pressure. A 25 Hertz high-pass filter 106 will pass the 40 Hz frequency components from the exciter, but will filter out many of the lower-frequency pulsatile components. The exciter can be a small speaker having an oscillating electrical input. In one embodiment, the exciter and detector can be at the same location.

FIG. 9 is a diagram of an apparatus 110 that uses the pressure transducer to produce the volume-indicative signal. This volume-indicative signal is filtered in the high-pass filter 106 and sent to processor 80.

FIG. 10 is a graph of the cross-sectional area versus the transmural pressure. If a constant high-frequency pressure component is applied at different baseline pressures, the high-frequency output in a volume-indicative signal will be the greatest at around zero transmural pressure, as shown in FIG. 10.

FIGS. 11A-C are graphs illustrating the operation of the apparatus of FIGS. 8 and 9. FIG. 11A is a graph of the arterial blood pressure with an imposed high-frequency component. As with all the arterial pressure graphs in the present invention, this graph is simplified for the purpose of clarity. FIG. 11B is a graph illustrating a filtered high-frequency component of the cross-sectional area obtained with a filtered plethysmograph signal or a filtered pressure transducer signal. FIG. 11C illustrates the amplitude of the high-frequency component of the volume or cross-sectional area indicative signal. Note that the amplitude is greatest at the point that the blood pressure equals the cuff pressure (transmural pressure approximately zero).

Note that by changing the cuff pressure, the diastolic or systolic pressure can be found. When the cuff pressure is reduced to the diastolic pressure, peak A will merge with peak B. When the cuff pressure is increased to the systolic pressure, peak B will merge with peak C.

Additionally, if the cuff pressure is greater than the systolic or less than the diastolic, the amplitude of the high-frequency component will be smaller and more constant without the peaks associated with a transmural pressure of around zero. Thus, the system of the present invention can use multiple iterations to ensure that the cuff pressure is between the systolic and diastolic.

FIG. 12 is a flow chart illustrating the operation of the processor 80 of FIG. 8. In step 112, the high-frequency component is induced onto a blood pressure signal with an exciter. In step 114, a signal indicative of the cross-sectional area is produced with the plethysmograph. This signal can be filtered in step 116 with a high-pass filter which filters out pulsatile frequency components. In step 118, the filtered signal can be sampled with an Analog-to-Digital converter, and then sent into the processor. Alternately, the plethysmograph signal itself can be sampled in step 120, and this sampled signal filtered within the processor to remove the pulsatile components in a step 122. In step 124, a time that the amplitude of the filter signal is a maximum is determined. The transmural pressure at this time is zero. Thus, the arterial blood pressure at this time is equal to the external pressure.

Another set of embodiments use a system identification approach. Typically, in system identification, a system is perturbed and a response is measured. For example, the compliance can be directly probed by perturbing the artery with either a pressure or volume perturbation and recording the resulting volume or pressure response.

One way to do this is to provide a constant amplitude high-frequency volume perturbation and record the resulting pressure response. An example of such an approach is described below with respect to FIG. 13. FIG. 13 is a diagram illustrating an apparatus 126 which uses a device 128 to produce a small constant amplitude change in the cuff volume. The volume of the cuff vibrates a small amount due to the induced volume change by the device 128. In a preferred embodiment, a standard oscillometric cuff 78 is modified to provide a constant volume perturbation. This modification consists of device 128 that preferably comprises a piezoelectric speaker (not shown) attached to the cuff such that the diaphragm of the speaker forms part of the outside wall of the cuff. Movement of the speaker diaphragm changes the volume of the cuff. The displacement of the cuff 78 is sensed by an accelerometer (not shown) that is used in a feedback circuit to control the displacement of the diaphragm and ensure that it is constant even when the pressure inside the cuff changes. The device 128 also could be a piston (not shown) attached to a rotating disk (not shown) to produce a constant volume change in the cuff 78.

The cuff 78 is inflated by a cuff engine 74 that can inflate the cuff to a predetermined pressure and then close a valve (not shown) to seal the cuff volume. The cuff engine 74 and valve are connected to the processor 80 by a serial cable. This allows the processor 80 to control the inflation of the cuff 78 and the closing of the valve.

The pressure inside the cuff 78 is sensed by a pressure transducer 76, such as Micro Switch Model No. 142PC15G, mounted inside the cuff. A processor 80 that is capable of capturing analog waveforms and performing mathematical computations is used to record and process the signals. This processor 80 could be a general purpose computer that has additional analog-to-digital hardware, or it could be a custom processor.

The device works as follows. The cuff 78 is wrapped around the patient's arm and secured with a Velcro™ strap. The processor 80 sends a signal to the cuff engine 74 to inflate the cuff 78 to some value between the systolic and diastolic pressure. The desired DC cuff pressure could be determined by either a previous blood pressure measurement, from the calibrated prediction of propagation velocity, tonometer or vascular unloading system, or it could be determined iteratively through successive attempts at measuring the pressure with the present invention. The piezoelectric speaker is activated at this point to provide the constant amplitude volume perturbation. This perturbation is typically a sinusoidal oscillation at about 25 Hertz, but could be a variety of waveforms. The amplitude of the recorded pressure signal will depend upon the compliance of the cuff. This compliance is largely determined by the compliance of the arm, since the arm is supporting one side of the cuff. The arm compliance is partially determined by the compliance of the artery. Thus, the pressure inside the cuff is partially determined by the compliance of the artery. When the artery compliance is a minimum, the pressure oscillation will be minimum. The processor 80 records the 25 Hertz pressure oscillations in the cuff for at least one cardiac cycle. The processor 80 then calculates the amplitude of this pressure oscillation as a function of time. This can be done in a variety of ways, the simplest of which is to calculate the peak-to-peak amplitude for each cycle (this is the difference between the minimum and maximum values of the pressure signal over a four-millisecond period). The time at which the pressure oscillation is a minimum indicates the time when the compliance is maximum and thus the time when the DC cuff pressure is approximately equal to the applied pressure.

It should be noted that this system identification approach to probing compliance can be accomplished in a number of ways. In this embodiment, the volume was oscillated and the resulting pressure was recorded. It is, of course, possible to perturb or oscillate the pressure, and measure the arterial volume oscillation response to find the peak in compliance. In addition, it is usually not necessary to control the perturbation signal, as illustrated in this embodiment. It is usually sufficient to measure the perturbation amplitude and track the ratio of the output response to the input response. It also should be noted that the relationship between the input and output need not be described by a simple ratio of amplitudes, but the relative phases can be accounted for by more complicated mathematical descriptions such as complex transfer functions, auto-regressive moving average (ARMA) models or other mathematical descriptions.

FIG. 14 is an illustration of the cross-sectional area versus transmural pressure. Notice that a constant amplitude high-frequency component of a cross-sectional area signal input produces the smallest high-frequency component pressure signal output when the baseline transmural pressure is at zero. This fact is used in the operation of the embodiment of FIG. 13.

FIGS. 15A-D illustrate the operation of the embodiment of FIG. 13. FIG. 15A shows a high-frequency volume signal which illustrates the change in the volume of a cuff. FIG. 15B illustrates the blood pressure. FIG. 15C illustrates a cuff pressure showing the imposed high-frequency component. FIG. 15D is a filtered high-frequency pressure transducer signal. This figure illustrates that the amplitude of this signal is lowest at the points at which the blood pressure is equal to the transmural pressure.

FIG. 16 illustrates a method of operation of the apparatus shown in FIG. 13. In step 130, high-frequency components are induced in the volume of the cuff used to produce the external pressure onto the artery. In step 132, a signal is produced from the pressure transducer indicative of the pressure in the cuff. In step 134, this signal is filtered to take out the constant and pulsatile components of a signal with a high-pass filter. In step 136, this filtered signal is sampled by an Analog-to-Digital converter (not shown) and sent to the processor. Alternatively, the pressure transducer signal can be sampled in step 138 and then sent to the processor. The processor can filter out the constant and pulsatile components of the sample signal in step 140. In step 142, the processor determines a time at which the amplitude of the filtered signal is at a minimum. At this time, the transmural pressure is zero.

Those skilled in the art will realize that other system identification embodiments can be used with the present invention. For example, although the above system measures a pressure response to a volume perturbation, it is also possible to have a pressure perturbation and measure a volume response. Additionally the perturbation need not be controlled or held constant. Measuring the perturbation is sufficient in most cases.

FIGS. 17 and 21 are diagrams that illustrate embodiments which use pressure wave velocity measurement systems. In FIG. 17, an apparatus 144 has a device for measuring the velocity of a high-frequency pressure oscillation along the artery comprising exciter 146 and detector 148. The system also includes a cuff 78 for applying external pressure to the artery, a cuff engine 74 to inflate the cuff 78 to a predetermined pressure, and a processor 80 to control the cuff engine 74 and capture and process the velocity signal.

The propagation velocity measuring device measures the velocity of propagation of a high-frequency pressure oscillation along the artery. The pressure oscillation is induced by an exciter 146 at one point in the artery and the propagated pressure oscillation is sensed at another point in the artery by a detector 148. The velocity of the propagation is calculated from the distance between the exciter 146 and the detector 148 and the difference in phase between the excitation and detection points. The velocity of the propagation is related to the arterial pressure. This device is described in much more detail in the below-referenced U.S. patent application Ser. No. 08/228,213 and its CIP's Ser. No. 08/561,923 and Ser. No. 08/556,547. The velocity measurement systems can operate at a variety of oscillation frequencies ranging from 100 to 1000 Hertz.

In a preferred embodiment, the propagation velocity system is placed on the forearm of the patient. The detector 148 is placed over the radial artery on the styloid process of the radial bone. The exciter 146 is placed approximately 5 cm proximal to the detector 148, also over the radial artery. The cuff 78 is wrapped around the patient's arm to cover the exciter 146 and detector 148 of the velocity measurement system. The cuff 78 can alternately be positioned in between the exciter 146 and detector 148.

The velocity of propagation of the high-frequency pressure oscillation is inversely related to the compliance of the artery, because as the artery compliance increases the velocity decreases. Since the arterial compliance has a peak at a transmural pressure of approximately zero, the propagation velocity will have a minimum at this transmural pressure.

The device works as follows. The processor sends a signal to the cuff engine 74 causing the cuff engine 74 to inflate to a predetermined pressure between the systolic and diastolic pressure. This DC cuff pressure could be determined by either a previous blood pressure measurement, from the calibrated prediction of propagation velocity, tonometer or vascular unloading system, or it could be determined iteratively through successive attempts at measuring the pressure with the present invention. The processor then records the signal from the propagation velocity measurement system for at least one cardiac cycle. The processor then determines the time during the cardiac cycle that the velocity was minimum. The time of this minimum velocity is the time when the applied pressure is approximately equal to the arterial pressure. Once this determination has been made, the cuff 78 can be deflated.

FIG. 18 illustrates the propagation wave velocity in the artery versus the transmural pressure. Note that this curve has a minimum at a transmural pressure of about zero. This means that the output velocity of the propagation wave will have a minimum when the transmural pressure is equal to zero.

FIGS. 19A and 19B are graphs illustrating the operation of the apparatus of FIG. 17. As shown in these graphs, when the arterial pressure is equal to the external pressure, the velocity of propagation will have a minimum value.

FIG. 20 is a flow chart illustrating the use of the apparatus of FIG. 17. In step 152, an exciter and detector 148 are used to produce an indication of the velocity of a pressure wave transferred through the artery. In step 154, an external pressure is applied which is between the systolic and diastolic pressure. In step 156, a minimum of the velocity measurement is used to obtain a time that the transmural pressure is equal to zero.

FIG. 21 is a diagram illustrating an apparatus 158 using an exciter 160 and a detector 162 which are not placed underneath the external pressure cuff. This system is a pressure/volume embodiment. These pressure/volume embodiments require two signals, one that is related to the arterial pressure, and one that is related to the arterial volume. The volume measurement should be taken in the region over which the external pressure is applied. The external pressure should be within the systolic and the diastolic pressure. Another example of a pressure/volume embodiment is discussed above with respect to FIGS. 5-7.

In the preferred embodiment, the cuff 78 is a standard oscillometric cuff such as that provided by Critikon for their Dinamap product. The cuff engine 74 is capable of inflating the cuff to a pressure up to 300 mmHg, and the pressure transducer 76 should have a range up to 300 mmHg and sufficient sensitivity to measure pressure changes as small as 0.1 mmHg. The processor 80 should be able to capture analog waveforms and perform mathematical computations.

The cuff engine 74 is preferably under the control of the processor 80 and has a valve (not shown) that can seal off the cuff 78 so that the volume of the cuff 78 can be fixed. This valve (not shown) should be under control of the processor 80.

The processor 80 can be a general-purpose computer, such as an IBM PC, with a multi-function input-output board, such as a National Instruments MIO-16 board. Alternately, a custom microprocessor could be used. Communication to the cuff engine can be by a serial connection between the processor and the cuff engine.

The propagation velocity measuring device measures the velocity of propagation of a high-frequency pressure oscillation along the artery. The pressure oscillation is induced by an exciter 160 at one part of the artery and the propagated pressure oscillation is sensed in another point along the artery by detector 162. The velocity of propagation is calculated from the distance between the exciter 160 and detector 162 and the difference in phase between the excitation and detection points.

Pressure wave velocity measurement systems are described in more detail in U.S. patent application Ser. No. 08/228,213 entitled "Apparatus and Method for Measuring an Induced Perturbation to Determine Blood Pressure" filed Apr. 15, 1994 (corresponding to International Publication WO95/28126), and its CIP's Ser. No. 08/561,923 entitled "Apparatus and Method for Measuring an Induced Perturbation to Determine a Physiological Parameter" and Ser. No. 08/556,547 entitled "Apparatus and Method for Measuring an Induced Perturbation to Determine a Physiological Parameter," which are incorporated herein by reference. These systems sometimes have amplitude indications which are available to obtain viscosity information as well.

In a preferred embodiment, the velocity measurement system could be placed over the radial artery on the forearm. The cuff can be wrapped around the wrist, just distal to the exciter.

This embodiment works as follows. The processor sends a signal to the cuff engine to inflate the cuff to some value between the systolic and diastolic pressure. This DC cuff pressure could be determined by a previous blood pressure measurement, from the calibrated prediction of propagation velocity, tonometer or vascular unloading system, or it can be determined iteratively through successive attempts at measuring the pressure with the present invention. Once the pressure in the cuff has been established, the cuff engine closes the valve that seals off the cuff, fixing the volume of air in the cuff.

With the cuff volume fixed, the pressure in the cuff will have a small pulsatile component that is related to the volume of the artery. The DC component of the cuff pressure can be removed by the processor, leaving the pulsatile component. This pulsatile component is related to the volume of the artery.

The processor simultaneously records the pulsatile portion of the cuff pressure and the propagation velocity. These two signals correspond to the volume-indicative signal and the pressure-indicative signal. The processor then determines the slope of the relationship between volume- and pressure-indicative signals by taking the difference between successive pairs of measurements. This slope is related to the compliance and is defined as ##EQU2## where V(k) is the volume-indicative signal at sample k, and P(k) is the pressure-indicative signal at sample k.

The time at which this quantity peaks is the time at which the applied pressure is approximately equal to the arterial pressure. Once the peak in compliance is found, the cuff pressure can be set to zero.

FIGS. 22A-D are graphs which illustrate the workings of the embodiment of FIG. 21. In FIG. 22B, the graph of the measured velocity is shown. Looking again at FIG. 21, the pressure wave velocity is measured in a region with no external pressure applied. This means that, as shown in FIG. 18, the transmural pressure will be equal to the arterial pressure, which ranges, for example, from about 80 mmHg to 120 mmHg. Thus the measured velocity will be proportional to the arterial pressure. The measured volume shown in FIG. 22C is measured in a pressure regime where an external pressure is applied by a cuff and where the external pressure is between the systolic and diastolic pressure. This means that the volume signal of FIG. 22C has at least one point where the transmural pressure is equal to zero. In a similar fashion to that described with respect to FIGS. 6A-D, a graph of the measured volume versus measured velocity can be produced. This graph will have the greatest rate of change at a measured velocity Velx, associated with a time Tx, at which the transmural pressure under the cuff is equal to zero or the arterial pressure everywhere is equal to the external applied cuff pressure. The known arterial pressure at measured velocity Velx can be used to calibrate the velocity/arterial-pressure curve.

FIG. 23 is a diagram showing apparatus 158 that illustrates an embodiment based upon the arterial closing pressures. In the embodiment shown in FIG. 23, an exciter 60 under the control of an oscillator 162 produces an excitation signal which is passed down the artery and detected by detector 164. The output of detector 164 is filtered, in the manner described in "Apparatus and Method for Measuring an Induced Perturbation to Determine Blood Pressure" International Publication WO 95/28126, to determine the portion of the high-frequency signal that passes through the artery. This filter removes the detected high-frequency components that pass through tissue other than the artery. Processor 80 uses the output of detector 164 to determine whether the artery is closed.

FIGS. 24A-C illustrate the operation of the embodiment shown in FIG. 23. FIG. 24A illustrates the arterial pressure. FIG. 24B illustrates the high-frequency components of the excitation onto the artery that is caused by the exciter 160. FIG. 24C illustrates the high-frequency component of the pressure wave passing through the artery to detector 164. Note that, at an artery closing pressure, the signal is reduced to zero or severely attenuated. The processor 80 can then determine that, at time T1, the transmural pressure is at the transmural pressure that causes the artery to close. Thus, the arterial pressure at time T1 is the cuff pressure plus the artery closing transmural pressure. In this manner, the arterial pressure at a given time can be determined.

The pressure can be can be applied in a variety of locations: over the detector or exciter; in the propagation region; just before the exciter or just after the detector. The different placements will show different responses in the propagated signal (positioning the pressure at the detector, in the propagation region or at the exciter will show attenuation, while positioning the pressure before the exciter or after the detector will show amplification because of reflections), but all could potentially be used to detect opening and/or closing.

FIG. 25 is a diagram illustrating an alternate embodiment of the present invention that operates to determine the time that an artery is opened or closed. In the embodiment shown in FIG. 25, a detector 166 is used to detect the arterial pulse signal.

FIGS. 26A-B are graphs illustrating the operation of the embodiment of FIG. 25. FIG. 26A illustrates the arterial pressure. FIG. 26B illustrates the pulse signal detected at detector 166. At an artery closing pressure, the signal is reduced to zero or severely attenuated. The processor 80 determines, at time T1, the transmural pressure is at the artery closing transmural pressure. In this manner, the arterial pressure at a given time can be determined. The pressure can be applied over the detector or before the detector.

FIG. 27 is a diagram of an apparatus 170 of the present invention using a plethysmograph to obtain an arterial volume indicative signal in two different cardiac cycles with two different external pressures. One of the external pressures is less than the diastolic pressure and the other transmural pressure is between the diastolic and the systolic pressure.

FIG. 28 is a graph illustrating the relationship between arterial volume and the transmural pressure.

FIGS. 29A-C are graphs illustrating the operation of the embodiment of FIG. 27. FIG. 29A illustrates the arterial pressure. At time To, the external pressure is set at 70 mmHg, a pressure below the diastolic. At time TL, the external pressure is set at 90 mmHg, a pressure between the diastolic and the systolic pressure. FIG. 29B shows volume-indicative signals from the plethysmograph. The top curve is the arterial volume-indicative measurement at a cuff pressure of 70 mmHg starting at time To. The bottom curve is the arterial volume-indicative measurement at a cuff pressure of 90 mmHg starting at time TL. The processor 80 stores the arterial volume-indicative measurements to compare measurements made at different cycles. Note that the arterial volume measurements are relatively linearly related from time +T1 to time +T2, this range corresponding to the arterial pressures above 90 mmHg. When the arterial pressures go below 90 mmHg, the volume-indicative output of the measurements starting at time TL drops sharply. As shown in FIG. 29C, the volume indications at different external pressures can be graphed against each other by the processor 80. A linear region of this graph corresponds to the region between time +T1 and time +T2. A non-linear region of this graph corresponds to the region between time +T2 and time +T3. The time that the arterial pressure equals the external pressure (90 mmHg) can be determined from this graph by processor 80. There is a change in the slope at the point that the transmural pressure is equal to zero. Note that it is also possible to use such a system with two plethysmographs, one having an external applied pressure and the other not.

Various details of the implementation and method are merely illustrative of the invention. It will be understood that various changes in such details may be within the scope of the invention, which is to be limited only by the appended claims. For instance, as discussed above, the present invention could use a relationship between the viscosity and a critical pressure (such as a transmural pressure equal to zero) to determine a blood pressure at a certain time. Or the detector could be placed in a location which would allow it to receive pressures which pass through not only the artery, but skin, muscle, bone, or other tissue. Alternately, for the induced signal cases, a non-linear transfer function, such as the arterial volume versus transmural pressure, can be used to produce harmonics which can be detected using a band-pass filter set at a multiple of the input frequency, to give a signal that could give information about a critical transmural pressure.

Additionally, measurement of the actual flow of the blood can be done with a Doppler flow detector. The blood flow is related to the arterial volume and pressure in such a manner that there is a critical value that can be detected as an event.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3090377 *Oct 30, 1961May 21, 1963Peter F SalisburyBlood pressure measurement
US3095872 *Nov 27, 1959Jul 2, 1963Cutler Hammer IncBlood pressure measurement
US4074711 *Sep 7, 1976Feb 21, 1978American Optical CorporationApparatus and process for determining systolic pressure
US4154238 *Dec 27, 1976May 15, 1979American Optical CorporationApparatus and process using second derivative of oscillometric waveform for producing sphygmometric information
US4172450 *May 25, 1977Oct 30, 1979Barr & Stroud LimitedMethod and apparatus for determining the instantaneous arterial blood pressure
US4343314 *Aug 11, 1980Aug 10, 1982Bohumir SramekNon-invasive real time blood pressure measurement system
US4349034 *Mar 31, 1980Sep 14, 1982Johnson & JohnsonAutomatic mean blood pressure reading device
US4524777 *May 5, 1983Jun 25, 1985Ueda Electronic Works LimitedAutomatic, continuous and indirect blood pressure measurement apparatus
US4646754 *Feb 19, 1985Mar 3, 1987Seale Joseph BNon-invasive determination of mechanical characteristics in the body
US4660566 *Nov 25, 1985Apr 28, 1987Fidelity Medical, Inc.Method and apparatus for the non-invasive monitoring of arterial blood pressure waves
US4699152 *Nov 13, 1986Oct 13, 1987Baxter Travenol Laboratories, Inc.Techniques for obtaining information associated with an individual's blood pressure including specifically a stat mode technique
US4771792 *Feb 19, 1986Sep 20, 1988Seale Joseph BNon-invasive determination of mechanical characteristics in the body
US4796184 *Aug 1, 1986Jan 3, 1989Cas Medical Systems, Inc.Automatic blood pressure measuring device and method
US4869261 *Mar 22, 1988Sep 26, 1989University J.E. Purkyne V BrneAutomatic noninvasive blood pressure monitor
US5148807 *Aug 28, 1990Sep 22, 1992Ohio State UniversityNon-contact tonometer
US5339818 *Sep 9, 1993Aug 23, 1994University Of Utah Research FoundationMethod for determining blood pressure utilizing a neural network
US5423322 *Apr 14, 1994Jun 13, 1995Medical Physics, Inc.Total compliance method and apparatus for noninvasive arterial blood pressure measurement
US5425372 *Jun 22, 1993Jun 20, 1995Takeda Engineering Consultant, Inc.Blood pressure measurement apparatus and associated method
US5447163 *Dec 13, 1993Sep 5, 1995Critikon, Inc.Peripheral arterial monitoring instruments
US5551440 *Feb 28, 1995Sep 3, 1996Omron CorporationElectronic blood pressure meter
Non-Patent Citations
Reference
1"Medwave: A New Choice: Vasotrac™ APM 205 Blood Pressure Monitor" Brochure; Medwave, Inc.; 1995.
2Gravlee, Glenn P., M.D. and Joni K. Brockschmidt; "Accuracy of Four Indirect Methods of Blood Pressure Measurement, With Hemodynamic Correlations"; Journal of Clinical Monitoring; vol. 6, No. 4; Oct., 1990; pp. 284-298.
3 *Gravlee, Glenn P., M.D. and Joni K. Brockschmidt; Accuracy of Four Indirect Methods of Blood Pressure Measurement, With Hemodynamic Correlations ; Journal of Clinical Monitoring ; vol. 6, No. 4; Oct., 1990; pp. 284 298.
4 *Medwave: A New Choice: Vasotrac APM 205 Blood Pressure Monitor Brochure; Medwave, Inc.; 1995.
5Ramsey, Maynard III, M.D., Ph.D.; "Blood Pressure Monitoring: Automated Oscillometric Devices"; Journal of Clinical Monitoring ; vol. 7, No. 1; Jan., 1991; pp. 56-67.
6 *Ramsey, Maynard III, M.D., Ph.D.; Blood Pressure Monitoring: Automated Oscillometric Devices ; Journal of Clinical Monitoring ; vol. 7, No. 1; Jan., 1991; pp. 56 67.
7Shimazu, H., et al.; "Vibration technique for indirect measurement of diastolic arterial pressure in human fingers"; Medical& Biological Engineering& Computing; Mar. 1989; pp. 130-136.
8 *Shimazu, H., et al.; Vibration technique for indirect measurement of diastolic arterial pressure in human fingers ; Medical & Biological Engineering & Computing ; Mar. 1989; pp. 130 136.
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Citing PatentFiling datePublication dateApplicantTitle
US6371921Nov 1, 1999Apr 16, 2002Masimo CorporationSystem and method of determining whether to recalibrate a blood pressure monitor
US6471655 *Jun 29, 1999Oct 29, 2002Vitalwave CorporationMethod and apparatus for the noninvasive determination of arterial blood pressure
US6554774 *Mar 23, 2000Apr 29, 2003Tensys Medical, Inc.Method and apparatus for assessing hemodynamic properties within the circulatory system of a living subject
US6626840 *Oct 29, 2001Sep 30, 2003Rutgers, The State University Of New JerseyMethod and system for detecting vascular conditions using an occlusive arm cuff plethysmograph
US6632181 *Oct 5, 1999Oct 14, 2003Masimo CorporationRapid non-invasive blood pressure measuring device
US6730038Feb 5, 2002May 4, 2004Tensys Medical, Inc.Method and apparatus for non-invasively measuring hemodynamic parameters using parametrics
US6850787Jun 26, 2002Feb 1, 2005Masimo Laboratories, Inc.Signal component processor
US6852083Jan 17, 2002Feb 8, 2005Masimo CorporationSystem and method of determining whether to recalibrate a blood pressure monitor
US6920345Jan 24, 2003Jul 19, 2005Masimo CorporationOptical sensor including disposable and reusable elements
US6934570Dec 19, 2002Aug 23, 2005Masimo CorporationPhysiological sensor combination
US6939305Oct 14, 2003Sep 6, 2005Masimo CorporationRapid non-invasive blood pressure measuring device
US6939306 *Sep 2, 2003Sep 6, 2005K-Jump Health Co., Ltd.Method for measuring blood pressure and pulse rate with a pump-less mechanical compression apparatus
US6961598Feb 21, 2003Nov 1, 2005Masimo CorporationPulse and active pulse spectraphotometry
US6979812Feb 24, 2005Dec 27, 2005Masimo CorporationSystems and methods for indicating an amount of use of a sensor
US6996427Dec 18, 2003Feb 7, 2006Masimo CorporationPulse oximetry data confidence indicator
US6999904Aug 5, 2002Feb 14, 2006Masimo CorporationVariable indication estimator
US7003338Jul 8, 2003Feb 21, 2006Masimo CorporationMethod and apparatus for reducing coupling between signals
US7024233Sep 16, 2004Apr 4, 2006Masimo CorporationPulse oximetry data confidence indicator
US7030749Oct 28, 2004Apr 18, 2006Masimo CorporationParallel measurement alarm processor
US7041060Sep 6, 2005May 9, 2006Masimo CorporationRapid non-invasive blood pressure measuring device
US7044918Oct 27, 2004May 16, 2006Masimo CorporationPlethysmograph pulse recognition processor
US7048691Mar 22, 2001May 23, 2006Tensys Medical, Inc.Method and apparatus for assessing hemodynamic parameters within the circulatory system of a living subject
US7074199 *Sep 12, 2001Jul 11, 2006Revivant CorporationCPR chest compression monitor and method of use
US7096054Jul 31, 2003Aug 22, 2006Masimo CorporationLow noise optical housing
US7118534 *Sep 21, 2001Oct 10, 2006Virginia Commonwealth UniversityMethods for monitoring and optimizing central venous pressure and intravascular volume
US7142901Nov 14, 2003Nov 28, 2006Masimo CorporationParameter compensated physiological monitor
US7149561Oct 28, 2003Dec 12, 2006Masimo CorporationOptical spectroscopy pathlength measurement system
US7186966Dec 19, 2005Mar 6, 2007Masimo CorporationAmount of use tracking device and method for medical product
US7190261Apr 18, 2006Mar 13, 2007Masimo CorporationArrhythmia alarm processor
US7225006Jan 23, 2003May 29, 2007Masimo CorporationAttachment and optical probe
US7225007Jun 30, 2005May 29, 2007Masimo CorporationOptical sensor including disposable and reusable elements
US7232412Dec 3, 2003Jun 19, 2007Omron Healthcare Co., Ltd.Blood pressure measuring apparatus
US7239905Aug 16, 2005Jul 3, 2007Masimo Laboratories, Inc.Active pulse blood constituent monitoring
US7245953Nov 5, 2002Jul 17, 2007Masimo CorporationReusable pulse oximeter probe and disposable bandage apparatii
US7254431Aug 30, 2004Aug 7, 2007Masimo CorporationPhysiological parameter tracking system
US7254434Oct 13, 2004Aug 7, 2007Masimo CorporationVariable pressure reusable sensor
US7272425Sep 26, 2005Sep 18, 2007Masimo CorporationPulse oximetry sensor including stored sensor data
US7274955Sep 25, 2003Sep 25, 2007Masimo CorporationParameter compensated pulse oximeter
US7280858Jan 4, 2005Oct 9, 2007Masimo CorporationPulse oximetry sensor
US7292883Mar 30, 2005Nov 6, 2007Masimo CorporationPhysiological assessment system
US7295866Feb 24, 2004Nov 13, 2007Masimo CorporationLow power pulse oximeter
US7332784Jun 27, 2006Feb 19, 2008Masimo CorporationMethod of providing an optoelectronic element with a non-protruding lens
US7340287Dec 2, 2005Mar 4, 2008Masimo CorporationFlex circuit shielded optical sensor
US7343186May 27, 2005Mar 11, 2008Masimo Laboratories, Inc.Multi-wavelength physiological monitor
US7355512Mar 13, 2007Apr 8, 2008Masimo CorporationParallel alarm processor
US7371981Feb 18, 2005May 13, 2008Masimo CorporationConnector switch
US7373193Nov 5, 2004May 13, 2008Masimo CorporationPulse oximetry data capture system
US7373194Feb 1, 2005May 13, 2008Masimo CorporationSignal component processor
US7377899May 3, 2006May 27, 2008Masimo CorporationSine saturation transform
US7415297Mar 8, 2005Aug 19, 2008Masimo CorporationPhysiological parameter system
US7428432Apr 22, 2003Sep 23, 2008Masimo CorporationSystems and methods for acquiring calibration data usable in a pulse oximeter
US7429250Jul 11, 2006Sep 30, 2008The Johns Hopkins UniversityCPR chest compression monitor and method of use
US7438683Mar 3, 2005Oct 21, 2008Masimo CorporationApplication identification sensor
US7440787Nov 28, 2005Oct 21, 2008Masimo Laboratories, Inc.Systems and methods for determining blood oxygen saturation values using complex number encoding
US7467002Aug 20, 2007Dec 16, 2008Masimo CorporationSine saturation transform
US7471969Nov 25, 2003Dec 30, 2008Masimo CorporationPulse oximeter probe-off detector
US7483729Nov 4, 2004Jan 27, 2009Masimo CorporationPulse oximeter access apparatus and method
US7483730Oct 4, 2004Jan 27, 2009Masimo CorporationLow-noise optical probes for reducing ambient noise
US7496391Jan 13, 2004Feb 24, 2009Masimo CorporationManual and automatic probe calibration
US7499835Mar 14, 2006Mar 3, 2009Masimo CorporationVariable indication estimator
US7500950Jul 23, 2004Mar 10, 2009Masimo CorporationMultipurpose sensor port
US7503896Mar 22, 2001Mar 17, 2009Tensys Medical, Inc.Method and apparatus for the noninvasive assessment of hemodynamic parameters including blood vessel location
US7509494Feb 28, 2003Mar 24, 2009Masimo CorporationInterface cable
US7526328Dec 15, 2006Apr 28, 2009Masimo CorporationManual and automatic probe calibration
US7530942Oct 18, 2006May 12, 2009Masimo CorporationRemote sensing infant warmer
US7530949Aug 3, 2004May 12, 2009Masimo CorporationDual-mode pulse oximeter
US7559894Sep 9, 2005Jul 14, 2009New Paradigm Concepts, LLCMultiparameter whole blood monitor and method
US7734320Aug 20, 2007Jun 8, 2010Masimo CorporationSensor isolation
US7761128Apr 13, 2005Jul 20, 2010Masimo CorporationPhysiological monitor
US7791155Dec 21, 2007Sep 7, 2010Masimo Laboratories, Inc.Detector shield
US7801581Dec 11, 2006Sep 21, 2010Masimo Laboratories, Inc.Optical spectroscopy pathlength measurement system
US7844314Feb 1, 2005Nov 30, 2010Masimo CorporationPhysiological measurement communications adapter
US7844315May 3, 2006Nov 30, 2010Masimo CorporationPhysiological measurement communications adapter
US7865222Jan 23, 2006Jan 4, 2011Masimo LaboratoriesMethod and apparatus for reducing coupling between signals in a measurement system
US7867170May 3, 2004Jan 11, 2011Tensys Medical, Inc.Method and apparatus for non-invasively measuring hemodynamic parameters using parametrics
US7873497Jan 29, 2009Jan 18, 2011Masimo CorporationVariable indication estimator
US7880606Feb 12, 2008Feb 1, 2011Masimo CorporationPhysiological trend monitor
US7880626Oct 12, 2006Feb 1, 2011Masimo CorporationSystem and method for monitoring the life of a physiological sensor
US7891355May 3, 2006Feb 22, 2011Masimo CorporationPhysiological monitor
US7894868May 5, 2006Feb 22, 2011Masimo CorporationPhysiological monitor
US7899507May 3, 2006Mar 1, 2011Masimo CorporationPhysiological monitor
US7904132Dec 16, 2008Mar 8, 2011Masimo CorporationSine saturation transform
US7910875Mar 6, 2007Mar 22, 2011Masimo CorporationSystems and methods for indicating an amount of use of a sensor
US7919713Apr 16, 2008Apr 5, 2011Masimo CorporationLow noise oximetry cable including conductive cords
US7937128Jun 30, 2005May 3, 2011Masimo CorporationCyanotic infant sensor
US7937129Mar 21, 2006May 3, 2011Masimo CorporationVariable aperture sensor
US7941199May 15, 2007May 10, 2011Masimo Laboratories, Inc.Sepsis monitor
US7962188Oct 12, 2006Jun 14, 2011Masimo CorporationRobust alarm system
US7976472Sep 6, 2005Jul 12, 2011Masimo CorporationNoninvasive hypovolemia monitor
US7988637May 3, 2006Aug 2, 2011Masimo CorporationPlethysmograph pulse recognition processor
US7991446May 8, 2006Aug 2, 2011Masimo CorporationSystems and methods for acquiring calibration data usable in a pulse oximeter
US8000761May 2, 2006Aug 16, 2011Masimo CorporationResposable pulse oximetry sensor
US8028701May 31, 2007Oct 4, 2011Masimo CorporationRespiratory monitoring
US8046040Apr 4, 2006Oct 25, 2011Masimo CorporationPulse oximetry data confidence indicator
US8048040Sep 11, 2008Nov 1, 2011Masimo CorporationFluid titration system
US8057400Jun 12, 2009Nov 15, 2011Angiologix, Inc.System and method of measuring changes in arterial volume of a limb segment
US8118620Oct 9, 2008Feb 21, 2012Masimo CorporationConnector assembly with reduced unshielded area
US8145287Apr 24, 2009Mar 27, 2012Masimo CorporationManual and automatic probe calibration
US8147433Feb 16, 2007Apr 3, 2012Johns Hopkins UniversityCPR chest compression monitor and method of use
US8182443Jan 17, 2007May 22, 2012Masimo CorporationDrug administration controller
US8203438Jul 28, 2009Jun 19, 2012Masimo CorporationAlarm suspend system
US8203704Aug 3, 2009Jun 19, 2012Cercacor Laboratories, Inc.Multi-stream sensor for noninvasive measurement of blood constituents
US8219172Mar 17, 2006Jul 10, 2012Glt Acquisition Corp.System and method for creating a stable optical interface
US8228181Jan 31, 2011Jul 24, 2012Masimo CorporationPhysiological trend monitor
US8233955Nov 29, 2006Jul 31, 2012Cercacor Laboratories, Inc.Optical sensor including disposable and reusable elements
US8244325May 29, 2007Aug 14, 2012Cercacor Laboratories, Inc.Noninvasive oximetry optical sensor including disposable and reusable elements
US8255026Oct 12, 2007Aug 28, 2012Masimo Corporation, Inc.Patient monitor capable of monitoring the quality of attached probes and accessories
US8255028May 5, 2006Aug 28, 2012Masimo Corporation, Inc.Physiological monitor
US8260577Jan 14, 2011Sep 4, 2012Masimo CorporationVariable indication estimator
US8265723Oct 12, 2007Sep 11, 2012Cercacor Laboratories, Inc.Oximeter probe off indicator defining probe off space
US8274360Oct 10, 2008Sep 25, 2012Masimo CorporationSystems and methods for storing, analyzing, and retrieving medical data
US8280473Oct 12, 2007Oct 2, 2012Masino Corporation, Inc.Perfusion index smoother
US8310336Oct 14, 2010Nov 13, 2012Masimo CorporationSystems and methods for storing, analyzing, retrieving and displaying streaming medical data
US8315683Sep 20, 2007Nov 20, 2012Masimo CorporationDuo connector patient cable
US8328727May 18, 2006Dec 11, 2012Tensys Medical, Inc.Method and apparatus for assessing hemodynamic parameters within the circulatory system of a living subject
US8337403Oct 20, 2008Dec 25, 2012Masimo CorporationPatient monitor having context-based sensitivity adjustments
US8346330Oct 12, 2009Jan 1, 2013Masimo CorporationReflection-detector sensor position indicator
US8353842Dec 23, 2008Jan 15, 2013Masimo CorporationPortable patient monitor
US8355766Oct 9, 2008Jan 15, 2013Masimo CorporationCeramic emitter substrate
US8364223May 3, 2006Jan 29, 2013Masimo CorporationPhysiological monitor
US8374665Apr 21, 2008Feb 12, 2013Cercacor Laboratories, Inc.Tissue profile wellness monitor
US8385995Aug 6, 2007Feb 26, 2013Masimo CorporationPhysiological parameter tracking system
US8398556Sep 30, 2008Mar 19, 2013Covidien LpSystems and methods for non-invasive continuous blood pressure determination
US8399822Mar 22, 2011Mar 19, 2013Masimo CorporationSystems and methods for indicating an amount of use of a sensor
US8401602Oct 12, 2009Mar 19, 2013Masimo CorporationSecondary-emitter sensor position indicator
US8405608Feb 28, 2008Mar 26, 2013Masimo CorporationSystem and method for altering a display mode
US8414499Dec 7, 2007Apr 9, 2013Masimo CorporationPlethysmograph variability processor
US8418524Jun 11, 2010Apr 16, 2013Masimo CorporationNon-invasive sensor calibration device
US8423106Mar 10, 2008Apr 16, 2013Cercacor Laboratories, Inc.Multi-wavelength physiological monitor
US8428967May 18, 2011Apr 23, 2013Cercacor Laboratories, Inc.Spot check monitor credit system
US8430817Oct 15, 2010Apr 30, 2013Masimo CorporationSystem for determining confidence in respiratory rate measurements
US8437825Jul 2, 2009May 7, 2013Cercacor Laboratories, Inc.Contoured protrusion for improving spectroscopic measurement of blood constituents
US8447374Oct 9, 2008May 21, 2013Ceracor Laboratories, Inc.Systems and methods for determining blood oxygen saturation values using complex number encoding
US8457703Nov 13, 2007Jun 4, 2013Masimo CorporationLow power pulse oximeter
US8457707Sep 19, 2007Jun 4, 2013Masimo CorporationCongenital heart disease monitor
US8463347Sep 30, 2009Jun 11, 2013Nellcor Puritan Bennett IrelandSystems and methods for normalizing a plethysmograph signal for improved feature analysis
US8471713Jul 22, 2010Jun 25, 2013Cercacor Laboratories, Inc.Interference detector for patient monitor
US8473020Jul 27, 2010Jun 25, 2013Cercacor Laboratories, Inc.Non-invasive physiological sensor cover
US8498684Mar 8, 2011Jul 30, 2013Masimo CorporationSine saturation transform
US8506498Oct 9, 2008Aug 13, 2013Nellcor Puritan Bennett IrelandSystems and methods using induced perturbation to determine physiological parameters
US8515509Aug 3, 2009Aug 20, 2013Cercacor Laboratories, Inc.Multi-stream emitter for noninvasive measurement of blood constituents
US8529301Feb 17, 2012Sep 10, 2013Masimo CorporationShielded connector assembly
US8532727Aug 20, 2007Sep 10, 2013Masimo CorporationDual-mode pulse oximeter
US8532728Dec 29, 2008Sep 10, 2013Masimo CorporationPulse oximeter probe-off detector
US8532751Sep 30, 2008Sep 10, 2013Covidien LpLaser self-mixing sensors for biological sensing
US8547209May 21, 2012Oct 1, 2013Masimo CorporationAlarm suspend system
US8548548Nov 29, 2010Oct 1, 2013Masimo CorporationPhysiological measurement communications adapter
US8548550Jul 31, 2012Oct 1, 2013Cercacor Laboratories, Inc.Optical sensor including disposable and reusable elements
US8560032May 22, 2012Oct 15, 2013Cercacor Laboratories, Inc.Noninvasive multi-parameter patient monitor
US8560245Nov 21, 2008Oct 15, 2013Nellcor Puritan Bennett IrelandContinuous non-invasive blood pressure measurement apparatus and methods providing automatic recalibration
US8570167Jul 24, 2012Oct 29, 2013Masimo CorporationPhysiological trend monitor
US8570503Jun 15, 2012Oct 29, 2013Cercacor Laboratories, Inc.Heat sink for noninvasive medical sensor
US8571618Sep 27, 2010Oct 29, 2013Cercacor Laboratories, Inc.Adaptive calibration system for spectrophotometric measurements
US8571619May 19, 2010Oct 29, 2013Masimo CorporationHemoglobin display and patient treatment
US8577431Jul 2, 2009Nov 5, 2013Cercacor Laboratories, Inc.Noise shielding for a noninvasive device
US8584345Mar 7, 2011Nov 19, 2013Masimo CorporationReprocessing of a physiological sensor
US8588880Feb 16, 2010Nov 19, 2013Masimo CorporationEar sensor
US8597195Jan 10, 2011Dec 3, 2013Tensys Medical, Inc.Method and apparatus for non-invasively measuring hemodynamic parameters using parametrics
US8600467Jul 1, 2010Dec 3, 2013Cercacor Laboratories, Inc.Optical sensor including disposable and reusable elements
US8606342Oct 31, 2005Dec 10, 2013Cercacor Laboratories, Inc.Pulse and active pulse spectraphotometry
US8628477Jul 31, 2009Jan 14, 2014Nellcor Puritan Bennett IrelandSystems and methods for non-invasive determination of blood pressure
US8630691Aug 3, 2009Jan 14, 2014Cercacor Laboratories, Inc.Multi-stream sensor front ends for noninvasive measurement of blood constituents
US8641631Apr 8, 2005Feb 4, 2014Masimo CorporationNon-invasive monitoring of respiratory rate, heart rate and apnea
US8652060Jan 22, 2008Feb 18, 2014Masimo CorporationPerfusion trend indicator
US8657755Oct 4, 2011Feb 25, 2014Angiologix, Inc.System and method of measuring changes in arterial volume of a limb segment
US8660799Oct 3, 2008Feb 25, 2014Nellcor Puritan Bennett IrelandProcessing and detecting baseline changes in signals
US8663107May 3, 2011Mar 4, 2014Cercacor Laboratories, Inc.Sepsis monitor
US8666468May 4, 2011Mar 4, 2014Masimo CorporationPatient monitor for determining microcirculation state
US8667967Sep 1, 2011Mar 11, 2014Masimo CorporationRespiratory monitoring
US8670811Jun 25, 2010Mar 11, 2014Masimo CorporationPulse oximetry system for adjusting medical ventilation
US8670814Jan 27, 2009Mar 11, 2014Masimo CorporationLow-noise optical probes for reducing ambient noise
US8676286Jan 3, 2011Mar 18, 2014Cercacor Laboratories, Inc.Method and apparatus for reducing coupling between signals in a measurement system
US8682407May 3, 2011Mar 25, 2014Masimo CorporationCyanotic infant sensor
US8688183Sep 2, 2010Apr 1, 2014Ceracor Laboratories, Inc.Emitter driver for noninvasive patient monitor
US8690799Oct 14, 2010Apr 8, 2014Masimo CorporationAcoustic respiratory monitoring sensor having multiple sensing elements
US8700112Feb 28, 2013Apr 15, 2014Masimo CorporationSecondary-emitter sensor position indicator
US8702627Oct 14, 2010Apr 22, 2014Masimo CorporationAcoustic respiratory monitoring sensor having multiple sensing elements
US8712494May 2, 2011Apr 29, 2014Masimo CorporationReflective non-invasive sensor
US8715206Oct 14, 2010May 6, 2014Masimo CorporationAcoustic patient sensor
US8718737Apr 2, 2012May 6, 2014Masimo CorporationMethod and apparatus for demodulating signals in a pulse oximetry system
US8720249Apr 11, 2013May 13, 2014Masimo CorporationNon-invasive sensor calibration device
US8721541Jan 18, 2013May 13, 2014Masimo CorporationPhysiological monitor
US8721542Aug 7, 2008May 13, 2014Masimo CorporationPhysiological parameter system
US8723677Oct 19, 2011May 13, 2014Masimo CorporationPatient safety system with automatically adjusting bed
US8740792Jul 8, 2011Jun 3, 2014Masimo CorporationPatient monitor capable of accounting for environmental conditions
US8747328Apr 29, 2011Jun 10, 2014Raytheon Bbn Technologies Corp.Continuous blood pressure monitoring
US8754776Jun 14, 2013Jun 17, 2014Cercacor Laboratories, Inc.Interference detector for patient monitor
US8755535Oct 14, 2010Jun 17, 2014Masimo CorporationAcoustic respiratory monitoring sensor having multiple sensing elements
US8755872Jul 27, 2012Jun 17, 2014Masimo CorporationPatient monitoring system for indicating an abnormal condition
US8761850Dec 21, 2012Jun 24, 2014Masimo CorporationReflection-detector sensor position indicator
US8764671Jun 26, 2008Jul 1, 2014Masimo CorporationDisposable active pulse sensor
US8771204Dec 21, 2009Jul 8, 2014Masimo CorporationAcoustic sensor assembly
US8781543Mar 26, 2012Jul 15, 2014Jpmorgan Chase Bank, National AssociationManual and automatic probe calibration
US8781549Aug 14, 2012Jul 15, 2014Cercacor Laboratories, Inc.Noninvasive oximetry optical sensor including disposable and reusable elements
US20110263990 *May 27, 2011Oct 27, 2011Masimo CorporationRapid non-invasive blood pressure measuring device
USRE42753Jul 2, 2009Sep 27, 2011Masimo Laboratories, Inc.Active pulse blood constituent monitoring
USRE44875Mar 14, 2011Apr 29, 2014Cercacor Laboratories, Inc.Active pulse blood constituent monitoring
CN1296007C *Dec 3, 2003Jan 24, 2007欧姆龙健康医疗事业株式会社Blood pressure measuring apparatus
EP1426008A1 *Oct 29, 2003Jun 9, 2004Omron Healthcare Co., Ltd.Blood pressure measuring apparatus
Classifications
U.S. Classification600/485, 600/500
International ClassificationA61B5/022
Cooperative ClassificationA61B5/02133, A61B5/022
European ClassificationA61B5/021D, A61B5/022
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